Methods of forming material on a substrate, and a method of forming a field effect transistor gate oxide on a substrate

ABSTRACT

The invention includes methods of forming material on a substrate and methods of forming a field effect transistor gate oxide. In one implementation, a first species monolayer is chemisorbed onto a substrate within a chamber from a gaseous first precursor. The first species monolayer is discontinuously formed over the substrate. The substrate having the discontinuous first species monolayer is exposed to a gaseous second precursor different from the first precursor effective to react with the first species to form a second species monolayer, and effective to form a reaction product of the second precursor with substrate material not covered by the first species monolayer. The substrate having the second species monolayer and the reaction product is exposed to a third gaseous substance different from the first and second precursors effective to selectively remove the reaction product from the substrate relative to the second species monolayer. Other implementations are contemplated.

TECHNICAL FIELD

This invention relates to methods of forming material on a substrate andto methods of forming a field effect transistor gate oxide on asubstrate.

BACKGROUND OF THE INVENTION

A continuing goal in integrated circuitry design is to make ever denser,and therefore smaller, circuit devices. This results in thinner layersand smaller geometries. Further, new deposition techniques and materialsare constantly being developed to enable circuit devices to be madesmaller than the previous generation.

One common circuitry device is a field effect transistor. Such includesa pair of conductive source/drain regions having a semiconductivechannel region received therebetween. A conductive gate is receivedproximate the channel region, with a gate dielectric layer beingreceived between the gate and the channel region. Application of asuitable voltage potential to the gate enables current to flow betweenthe source/drain regions, with the transistor being capable ofessentially functioning as a switch.

A common material for the gate dielectric layer is silicon dioxide.However as device geometry continues to shrink, the thinness of the gatedielectric layer will likely preclude silicon dioxide from being used asa gate dielectric material due to its too small of a dielectricconstant. Accordingly, other dielectric materials with higher dielectricconstants have been proposed for use as gate dielectric layers.Exemplary such materials include Al₂O₃ (typically having a dielectricconstant of about nine), and HfO₂ (typically having a dielectricconstant ranging from about 18 to about 25).

Even high dielectric constant materials will most likely be deposited tovery thin thicknesses (for example 10 Angstroms or less) to achievedesired circuit densities. One comparatively new technique fordepositing very thin layers is atomic layer deposition (ALD). Describedin summary, ALD includes exposing an initial substrate to a firstgaseous precursor-chemical species to accomplish chemisorption of thespecies onto the substrate. Ideally, the chemisorption would form amonolayer that is uniformly one atom or molecule thick on the entireexposed initial substrate. Alternately considered and desirably, asaturated monolayer is formed. However more typically, chemisorptiondoes not occur on all portions of the substrate such that the monolayeris discontinuously formed thereover. Nevertheless, such a monolayer isstill considered a monolayer in the context of this document.

The first chemical precursor is purged from the substrate and a secondgaseous precursor is provided to enable a second species to chemisorbonto and with the first monolayer. Any remaining of the second gaseousprecursor is then purged and the steps are repeated, with exposure ofthe second species monolayer to the first gaseous precursor. In someinstances, the two monolayers may be of the same species. Also, a thirdspecies or more from additional gaseous precursors may be successivelychemisorbed and purged, as described for the first and secondprecursors. Further, it is noted that one or more of the first, secondand third precursors can be mixed with an inert gas to speed up pressuresaturation within a reaction chamber. Purging may involve a variety oftechniques including, but not limited to, contacting the substrateand/or monolayer with a carrier gas and/or lowering pressure.

ALD is often described as a self-limiting process in that a finitenumber of sites exist on a substrate to which the first species may formchemical bonds. The second species might only bond to the first species,and thus may also be self-limiting. Once all of the finite number ofcites on a substrate are bonded with the first species, the firstspecies will often not bond to other of the first species already bondedwith the substrate.

One common semiconductive channel material is silicon, for examplemonocrystalline and/or polycrystalline silicon. When forming HfO₂ orAl₂O₃ by ALD, the second gaseous precursor will typically containoxygen, for example O₂, O₃ and/or H₂O. In many instances, exposure of asilicon channel to a first species containing hafnium or aluminum willnot completely saturate (meaning cover) all of the exposed siliconsurface. Accordingly, at the conclusion of a purge cycle, some siliconwill still typically be outwardly exposed. Typically, exposure of thisexposed silicon to an oxygen containing precursor will undesirably formsilicon dioxide from the exposed substrate material, as well as createhafnium oxide or aluminum oxide from the discontinuously adheredmonolayer. The result can be the formation of undesired silicon dioxidein combination with the hafnium oxide and/or aluminum oxide. This canresult in an unacceptable lowering of the dielectric constant of thelayer being formed, precluding its use in very thin gate dielectriclayers.

While the invention was motivated in addressing the above identifiedissues, it is in no way so limited. The invention is only by theaccompanying claims as literally worded, without interpretative or otherlimiting reference to the specification, and in accordance with thedoctrine of equivalents.

SUMMARY

The invention includes methods of forming material on a substrate andmethods of forming a field effect transistor gate oxide on a substrate.In one implementation, a method of forming material on a substrateincludes positioning a substrate within a deposition chamber. A firstspecies monolayer is chemisorbed onto the substrate within the chamberfrom a gaseous first precursor. The first species monolayer isdiscontinuously formed over the substrate. The substrate having thediscontinuous first species monolayer is exposed to a gaseous secondprecursor different from the first precursor effective to react with thefirst species to form a second species monolayer, and effective to forma reaction product of the second precursor with substrate material notcovered by the first species monolayer. The substrate having the secondspecies monolayer and the reaction product is exposed to a third gaseoussubstance different from the first and second precursors effective toselectively remove the reaction product from the substrate relative tothe second species monolayer.

In one implementation, a method of forming material on a substrateincludes positioning a substrate within a deposition chamber. A firstspecies monolayer is chemisorbed onto the substrate within the chamberfrom a gaseous precursor “a”. The substrate having the first speciesmonolayer is exposed to a gaseous precursor “b” different from precursor“a” effective to react with the first species to form a second speciesmonolayer. The exposing leaves some undesired impurity remaining on thesubstrate. The substrate having the undesired impurity is exposed to agaseous substance “c” different from the precursors “a” and “b”effective to selectively remove the undesired impurity from thesubstrate relative to the second species monolayer.

Other aspects and implementations are contemplated.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic view of a substrate at a processing step inaccordance with an aspect of the invention.

FIG. 2 is a view of the FIG. 1 substrate at a processing step subsequentto that shown by FIG. 1.

FIG. 3 is a view of the FIG. 2 substrate at a processing step subsequentto that shown by FIG. 2.

FIG. 4 is a view of the FIG. 3 substrate at a processing step subsequentto that shown by FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

The invention includes methods of forming material on a substrate, andin one preferred embodiment, methods of forming a fieldeffect-transistor gate oxide on a substrate. A substrate to be depositedupon would be positioned within any suitable deposition chamber, whetherexisting or yet-to-be developed. Any suitable chamber can be utilized,whether hot or cold walled, with subatmospheric chambers being mostpreferred. An exemplary typical deposition chamber would be a singlewafer processor having a plurality of gas inlets which feed to ashowerhead positioned to be received over a substrate to be depositedupon. One exemplary substrate is a semiconductive substrate, for examplea bulk monocrystalline silicon wafer. In the context of this document,the term “semiconductor substrate” or “semiconductive substrate” isdefined to mean any construction comprising semiconductive material,including, but not limited to, bulk semiconductive materials such as asemiconductive wafer (either alone or in assemblies comprising othermaterials thereon), and semiconductive material layers (either alone orin assemblies comprising other materials). The term “substrate” refersto any supporting structure, including, but not limited to, thesemiconductive substrates described above.

In one implementation, a first species monolayer is chemisorbed onto thesubstrate within the chamber from a gaseous first precursor, with thefirst species monolayer being discontinuously formed over the substrate.A preferred example is a metal containing first species monolayer. Byway of example only, FIG. 1 diagrammatically depicts a substrate 10having a first species monolayer 12 discontinuously formed thereover. Inthe exemplary described example, substrate 10 comprises substratematerial 14 which, in one preferred embodiment, will comprise a channelregion of a field effect transistor being formed. The material beingdeposited thereover will form a field effect transistor gate oxide. Anexemplary preferred material 14 is monocrystalline or polycrystallinesilicon. In the depicted example, a first species monolayer in the formof HfCl_(x) is discontinuously adhered to substrate material 14. Suchcan result from suitable exposure of substrate 14 to HfCl_(x), with “x”in such case being less than 5. Accordingly in this example, the gaseousfirst precursor and the first species monolayer comprise hafnium. By wayof example only, an alternate example would include a gaseous firstprecursor and first species monolayer comprising aluminum. For example,exposing a suitable substrate to trimethylaluminum (Al[CH₃]₃) can leavea discontinuous first species monolayer comprising Al(CH₃)_(x).

The substrate having the discontinuous first species monolayer isexposed to a gaseous second precursor different from the first precursoreffective to react with the first species to form a second speciesmonolayer, and effective to form a reaction product of the secondprecursor with substrate material not covered by the first speciesmonolayer. For example, FIG. 2 illustrates exposure of the substrate toa gaseous oxygen containing second precursor O₃ forming a second speciesmonolayer 16 in the form of HfO_(x) discontinuously formed over thesubstrate. “x” will typically be 2 or less than 2. Substrate material 14not covered by first species monolayer 12 (FIG. 1) has reacted with thegaseous second precursor to form a reaction product in the form of asilicon oxide designated as SiO_(x). Again, “x” will typically be 2 orless than 2. In one embodiment, the HfO_(x) will predominatelyconstitute the dioxide HfO₂, and the SiO_(x) will typically form thedioxide form of SiO₂ also. In an alternate example, the reaction productmight comprise a dioxide and the second species monolayer might comprisean oxide other than a dioxide. For example, where the first speciesmonolayer comprises Al(CH₃)_(x), the reaction product will stilltypically comprise SiO₂, and with the second species monolayercomprising Al₂O₃.

The substrate having the second species monolayer and the reactionproduct is exposed to a third gaseous substance different from the firstand second precursors effective to selectively remove the reactionproduct from the substrate relative to the second species monolayer.With respect to the exemplary depicted hafnium oxide being formed, FIG.3 illustrates exposure of the FIG. 2 substrate to such a third gaseoussubstance which has selectively removed the SiO_(x) from the substraterelative to the remaining HfO_(x). Exemplary preferred third gaseoussubstances to effect such selective removing includes fluorinecomprising gases. Further, an example includes a halide, for example ahydrogen halide such as HF. Alternate exemplary gases include F₂ andCHF₄, by way of example only. Such materials are also believed to besuitably usable in etching silicon dioxide selectively relative toAl₂O₃. In the context of this document, “selective removal” refers to aremoval rate of the material being removed at a rate of at least 2:1 tothe material remaining.

Referring to FIG. 4, the substrate has again been exposed to the gaseousfirst precursor to form a HfCl_(x) first species monolayer 18 which isillustrated as adhering to the oxygen of the HfO_(x) groups as well asto the previous unadhered sites of substrate material 14. The substratecould be subsequently exposed to the second gaseous precursor to form asecond species monolayer of the desired composition of the materialbeing formed. Processing might then continue by exposure of thesubstrate to the third gaseous substance to remove any subsequentlyformed undesired reaction product. Alternately or additionally,subsequent processing might be conducted which only constitutes repeatedcycling of the gaseous first precursor and the gaseous second precursorto form a thicker layer of material. Further alternately by way ofexample only, alternate or different alternating deposition precursorsmight be utilized, or switching to a deposition mode having a filmgrowth rate which is a non-ALD process regime and approximates more thatof a chemical vapor deposition process scheme.

FIG. 4 might be considered as illustrating the HfCl_(x) precursor ashaving an essential equal affinity to chemisorb to sites of substrate 14and monolayer 16. In one preferred implementation, the first gaseousprecursor (for example here HfCl_(x)) during the repeated chemisorbingpreferentially adsorbs to substrate material other than the secondspecies monolayer. For example, the HfCl_(x) might have greater affinityto adsorb to, and therefor preferentially adsorbs to, substrate material14 (i.e., silicon) than to second species monolayer material 16 (i.e.,HfO_(x)). In the context of this document, a preferential adsorption toone material vs. another material is at any atomic deposition ratiowhich is greater than 1:1. In one preferred implementation, thepreferential adsorbing is at a ratio of at least 2:1. In other words inthe illustrated example, twice as many HfCl_(x) molecular species wouldadhere to substrate material 14 as would adhere to the HfO_(x) materialof monolayer 16 over some given initial time period. Of course even withsuch a preferential adsorbing rate, the substrate might be exposed tothe precursor a sufficient period of time that substantial saturationoccurs and/or the preferential adsorbing effect is not seen/apparent inthe monolayer at the conclusion of that cycle of exposure to theprecursor.

The invention also contemplates a method of forming material on asubstrate independent or regardless of forming a discontinuous firstspecies monolayer. Specifically in one implementation, a substrate ispositioned within a deposition chamber. A first species monolayer ischemisorbed onto the substrate within the chamber from some gaseousprecursor “a”. The substrate having a first species monolayer is exposedto some gaseous precursor “b” different from precursor “a” effective toreact with the first species to form a second species monolayer, withsuch exposing leaving some undesired impurity on the substrate. By wayof example only and with respect to HfO₂ and Al₂O₃ formation, any of theabove-described examples are contemplated independent ofcontinuous/saturated vs. discontinuous first species monolayerformation, and independent of a reaction product forming from underlyingsubstrate.

Regardless, the substrate having the undesired impurity is exposed to agaseous substance “c” different from the precursors “a” and “b”effective to selectively remove the undesired impurity from thesubstrate relative to the second species monolayer. The gaseoussubstance “c” does not deposit material/another species onto thesubstrate. For example, consider the above-described deposition of Al₂O₃from trimethylaluminum and any suitable oxygen species, and independentof whether complete or discontinuous coverage of the first speciesmonolayer occurs. Consider that the exposure to a suitable oxygencontaining species leaves carbon as an undesired impurity on thesubstrate after exposure to the oxygen containing species. Accordingly,the undesired impurity remaining on the substrate (some carboncontaining species) is derived from the first species monolayer. Anexemplary gaseous substance “c” different from the precursors “a” and“b” would be HF (or CF₄ plus O₃, or F₂ plus O₃) which would selectivelyremove the carbon containing species from the substrate selectivelyrelative to the Al₂O₃ which was formed. Of course, alternate hydrogenhalides, alternate halogen containing gases including alternate fluorinecontaining gaseous substances “c” might be utilized. Other alternategaseous substances “c” are also of course contemplated. Further, gaseoussubstance “c” might be followed by a gaseous substance “d” (differentfrom “a”, “b” and “c”) for example effective to remove any adversereaction product from the substrate that might have been formed byexposure to “c”, for: example SiO₂ formed be exposure to oxygen in thisspecific example.

Further by way of example only, consider deposition of TiN from agaseous first precursor comprising TiCl₄ and a gaseous second precursorcomprising NH₃. A possible undesired impurity remaining on the substrateat the conclusion of exposure to the gaseous second precursor mightinclude a chlorine containing species. An exemplary possible gaseoussubstance “c” which would be effective to selectively remove anundesired chlorine containing impurity from the substrate relative to asecond species monolayer comprising TiN would include any of H₂,diborane and hydrazine. Accordingly, independent of discontinuous firstspecies monolayer formation and independent of reaction of the secondprecursor with exposed underlying substrate material, the inventioncontemplates removal of an undesired impurity by exposure to a gaseoussubstance “c” different from the precursors “a” and “b” effective toselectively remove the undesired impurity from the substrate relative tothe second species monolayer.

As the artisan will appreciate, any suitable temperatures, pressures,pulse times and flow rates might be utilizable in conjunction with thepractice of the above-described preferred embodiments. By way of exampleonly, typical preferred substrate temperatures will be anywhere fromroom temperature to 900° C., with a temperature range of from 100° C. to600° C. being a more preferred example. Pressure will typically besubatmospheric more preferably at or below 100 Torr, and most preferablyat or below 20 Torr. Exemplary preferred pulse times for the subjectexposure to the precursors and gaseous substances are anywhere from 0.2second to 5 seconds, with less than or equal to 1.0 second being mostpreferred. Any suitable flow rates can be utilized for the respectivegases and intermediate purge flows, or the absence of intermediate gaspurge flows being utilized. Plasma could, of course, be utilized in anyof the above-described processing, and whether generated within thedeposition chamber or remote therefrom.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of forming material on a substrate, comprising: positioninga substrate within a deposition chamber; chemisorbing a first speciesmonolayer onto the substrate within the chamber from a gaseous firstprecursor, the first species monolayer being discontinuously formed overthe substrate; exposing the substrate having the discontinuous firstspecies monolayer to a gaseous second precursor different from the firstprecursor effective to react with the first species to form a secondspecies monolayer and effective to form a reaction product of the secondprecursor with substrate material not covered by the first speciesmonolayer; and, exposing the substrate, having the second speciesmonolayer and the reaction product to a third gaseous substancedifferent from the first and second precursors effective to selectivelyremove the reaction product from the substrate relative to the secondspecies monolayer.
 2. The method of claim 1 wherein the reaction productis silicon dioxide formed from reaction of the gaseous second precursorwith silicon substrate material.
 3. The method of claim 2 wherein thethird gaseous substance comprises a halide.
 4. The method of claim 2wherein the third gaseous substance comprises a hydrogen halide.
 5. Themethod of claim 2 wherein the third gaseous substance comprisesfluorine.
 6. The method of claim 1 wherein the reaction product andsecond species each comprise an oxide.
 7. The method of claim 6 whereineach of the reaction product and the second species respectivelycomprises a dioxide.
 8. The method of claim 6 wherein the reactionproduct comprises a dioxide and the second species monolayer comprisesan oxide other than a dioxide.
 9. The method of claim 1 wherein thegaseous first precursor and the first species monolayer comprisehafnium.
 10. The method of claim 1 wherein the gaseous first precursorand the first species monolayer comprise hafnium, the second precursorcomprises oxygen, and the second species monolayer comprises an oxide ofhafnium.
 11. The method of claim 1 wherein the gaseous first precursorand the first species monolayer comprise aluminum.
 12. The method ofclaim 1 wherein the gaseous first precursor and the first speciesmonolayer comprise aluminum, the second precursor comprises oxygen, andthe second species monolayer comprises an oxide of aluminum.
 13. Themethod of claim 1 further comprising after conducting a cycle of thechemisorbing, the exposing to the second gaseous precursor and theexposing to the third gaseous substance, exposing the substrate to thefirst gaseous precursor, then the second gaseous precursor and withoutexposing the substrate to the third gaseous substance for at least onecycle.
 14. The method of claim 1 further comprising repeating thechemisorbing, the exposing to the second gaseous precursor and theexposing to the third gaseous substance.
 15. The method of claim 14further comprising after said repeating at least one cycle, exposing thesubstrate to the first gaseous precursor, then the second gaseousprecursor and without exposing the substrate to the third gaseoussubstance for at least one cycle.
 16. The method of claim 14 wherein thefirst gaseous precursor during said repeated chemisorbing preferentiallyadsorbs to substrate material other than the second species monolayer.17. The method of claim 16 wherein said preferentially adsorbing is at aratio of at least 2:1.
 18. The method of claim 16 wherein saidpreferential adsorbing is apparent at conclusion of said repeatedchemisorbing.
 19. A method of forming a field effect transistor gateoxide on a substrate, comprising: positioning a substrate within adeposition chamber; chemisorbing a first metal containing speciesmonolayer onto the substrate within the chamber from a gaseous firstprecursor, the first metal containing species monolayer beingdiscontinuously formed over the substrate; exposing the substrate havingthe discontinuous first metal containing species monolayer to a gaseousoxygen containing second precursor different from the first precursoreffective to react with the first metal containing species to form agate dielectric second metal oxide monolayer and effective to form anoxide reaction product of the oxygen containing second precursor withsubstrate material not covered by the first metal containing speciesmonolayer; and exposing the substrate having the gate dielectric secondmetal oxide monolayer and the oxide reaction product to a halogencontaining third gaseous substance different from the first and secondprecursors effective to selectively remove the oxide reaction productfrom the substrate relative to the gate dielectric second metal oxidemonolayer.
 20. The method of claim 19 wherein the oxide reaction productis silicon dioxide formed from reaction of the gaseous oxygen containingsecond precursor with silicon substrate material.
 21. The method ofclaim 19 wherein the third gaseous substance comprises a hydrogenhalide.
 22. The method of claim 19 wherein the halogen comprisesfluorine.
 23. The method of claim 19 wherein each of the oxide reactionproduct and the second species respectively comprises a dioxide.
 24. Themethod of claim 19 wherein the oxide reaction product comprises adioxide and the second metal oxide monolayer comprises an oxide otherthan a dioxide.
 25. The method of claim 19 wherein the gaseous firstprecursor and the first metal containing species monolayer comprisehafnium, and the second metal oxide monolayer comprises an oxide ofhafnium.
 26. The method of claim 19 wherein the gaseous first precursorand the first metal containing species monolayer comprise aluminum, andthe second metal oxide monolayer comprises an oxide of aluminum.
 27. Themethod of claim 19 further comprising after conducting a cycle of thechemisorbing, the exposing to the gaseous oxygen containing secondprecursor and the exposing to the halogen containing third gaseoussubstance, exposing the substrate to the first gaseous precursor, thenthe second gaseous precursor and without exposing the substrate to thethird gaseous substance for at least one cycle.
 28. A method of formingmaterial on a substrate, comprising: positioning a substrate within adeposition chamber; chemisorbing a first species monolayer onto thesubstrate within the chamber from a gaseous precursor “a”, exposing thesubstrate having the first species monolayer to a gaseous precursor “b”different from precursor “a” effective to react with the first speciesto form a second species monolayer, the exposing leaving some undesiredimpurity remaining on the substrate; and exposing the substrate havingthe undesired impurity to a gaseous substance “c” different from theprecursors “a” and “b” effective to selectively remove the undesiredimpurity from the substrate relative to the second species monolayer.29. The method of claim 28 wherein the first species monolayer isdiscontinuously formed over the substrate prior to the exposing to thegaseous precursor “b”.
 30. The method of claim 28 wherein the undesiredimpurity remaining on the substrate is derived from the first speciesmonolayer.
 31. The method of claim 28 wherein the undesired impurityremaining on the substrate is carbon derived from the first speciesmonolayer.
 32. The method of claim 28 wherein the undesired impurityremaining on the substrate is carbon derived from the first speciesmonolayer, and gaseous substance “c” comprises a hydrogen halide. 33.The method of claim 28 wherein the undesired impurity remaining on thesubstrate is carbon derived from the first species monolayer, andgaseous substance “c” comprises fluorine.
 34. The method of claim 28wherein the undesired impurity remaining on the substrate is a halogenderived from the first species monolayer.
 35. The method of claim 28wherein the undesired impurity remaining on the substrate is a halogenderived from the first species monolayer, and gaseous substance “c”comprises H₂.
 36. The method of claim 28 wherein the undesired impurityremaining on the substrate is a halogen derived from the first speciesmonolayer, and gaseous substance “c” comprises diborane.
 37. The methodof claim 28 wherein the undesired impurity remaining on the substrate isa halogen derived from the first species monolayer, and gaseoussubstance “c” comprises hydrazine.
 38. The method of claim 28 whereinthe material comprises Al₂O₃, gaseous precursor “a” comprisestrimethylaluminum, gaseous second precursor “b” comprises oxygen, theundesired impurity comprises carbon, and gaseous substance “c” comprisesa halogen.
 39. The method of claim 38 wherein gaseous substance “c”comprises a hydrogen halide.
 40. The method of claim 28 wherein thematerial comprises TiN, gaseous precursor “a” comprises TiCl₄, gaseoussecond precursor “b” comprises ammonia, the undesired impurity compriseschlorine, and gaseous substance “c” comprises H₂.
 41. The method ofclaim 28 wherein the material comprises TiN, gaseous precursor “a”comprises TiCl₄, gaseous second precursor “b” comprises ammonia, theundesired impurity comprises chlorine, and gaseous substance “c”comprises diborane.
 42. The method of claim 28 wherein the materialcomprises TiN, gaseous precursor “a” comprises TiCl₄, gaseous secondprecursor “b” comprises ammonia, the undesired, impurity compriseschlorine, and gaseous substance “c” comprises hydrazine.
 43. The methodof claim 28 further comprising after exposing the substrate to gaseoussubstance “c”, exposing the substrate to a gaseous substance “d”different from “a”, “b” and “c” effective to remove a reaction productfrom the substrate formed by exposure to “c”.